1. Field
The present invention relates to charge pumping, and more particularly to charge pump systems, methods and circuitry related to multilevel flash memory systems.
2. Description of Related Information
Conventional mixed mode integrated circuit systems frequently use different voltage supplies. Additionally, some aspects of analog signal processing, such as amplification, comparison, and pulse generation, may further require performance at higher voltages. In flash memories, erase, programming, and read signals are required for operation of memory cells. These erase, programming, and read signals often require voltage levels greater than a supply voltage. For example, an erase signal of 12-15 volts may be required from a supply voltage of 3 volts. Charge pumps may be used to generate the erase signal, the programming signal, and the read signal at the higher voltage levels. Also in multilevel volatile memories, the variation of the voltage level of the signal falls in a smaller range for the multibit signals stored in the memory cells.
Furthermore, many existing charge pumps include pump stages that are not sufficiently isolated from deleterious effect of neighboring pump stages. Thus, in sum, there is a need for charge pumps having fast rise time, efficient charge pumping, and/or that have pump stages capable of maintain signal levels and/or states even when adjacent or associated stages discharge, for example, to low level.